Problem: Tiffany has taken 5 quizzes and her average score so far is 84. If she gets 100, a perfect score, on the remaining 3 quizzes, what will her new average be?
If she gets 100 on the remaining quizzes, the sum of her scores will be $5 \cdot 84 + 3 \cdot 100 = 720$ Her overall average will then be $720 \div 8 = 90$.